Rogers Radix Printable Dielectric for 3D RF PCBs

What Is Rogers Radix Printable Dielectric?

Rogers Radix printable dielectric is an additive-manufacturing dielectric ink system designed specifically for building three-dimensional RF and microwave structures. It delivers a dielectric constant (Dk) of approximately 2.8 and a dissipation factor (Df) below 0.005 at 10 GHz, remaining stable well into the millimeter-wave range. Unlike conventional laminates that constrain designers to flat, planar geometries, Radix lets you print volumetric features—dielectric lenses, impedance-matching layers, waveguide fills, and graded-index structures—directly onto substrates or within hybrid stackups.

The material is dispensed through precision extrusion or jetting heads, then cured to form a solid dielectric body. Because thickness and fill pattern are digitally controlled layer by layer, you can vary the effective permittivity across the structure simply by adjusting infill density—something impossible with a traditional laminate sheet.

Key Electrical and Mechanical Properties

The Dk of 2.8 sits between low-Dk PTFE laminates like Taconic TLY-5 (Dk 2.20) and mid-range materials such as Isola Astra MT77 (Dk 3.00). That middle ground is useful: it is low enough to keep conductor losses manageable yet high enough to shrink wavelength for compact 3D features.

Why Additive Dielectrics Matter for RF Design

Traditional RF PCB design is inherently two-dimensional. Even complex multilayer stackups are built from flat sheets of laminate and prepreg. This limits what you can do with the dielectric volume between conductors. Radix printable dielectric breaks that constraint in several important ways:

• Graded-index (GRIN) lenses: By varying infill density from the center to the edge, you create a smooth permittivity gradient that focuses or steers a beam without a shaped surface—critical for compact 5G and 77 GHz automotive radar antennas.
• Integrated waveguide fills: Substrate-integrated waveguide (SIW) cavities can be filled with a precisely controlled dielectric, reducing cavity dimensions by a factor of 1/√Dk compared to air.
• Impedance-matching layers: A printed quarter-wave transformer layer with a specific effective Dk can match a radiating element to free space more smoothly than a single-Dk slab.
• Conformal and non-planar builds: Printing dielectric onto curved surfaces enables conformal antenna arrays on vehicle bodies or aircraft skins.

Wavelength in Radix Dielectric

Knowing the guided wavelength inside the printed dielectric is the starting point for dimensioning any 3D RF feature. The wavelength in a dielectric is λ_d = λ₀ / √Dk, where λ₀ is the free-space wavelength. At 28 GHz (a key 5G FR2 band), the free-space wavelength is about 10.7 mm; inside solid Radix (Dk ≈ 2.8) that shrinks to roughly 6.4 mm. At 77 GHz for automotive radar, the in-dielectric wavelength drops to about 2.3 mm.

Use the calculator below to find the wavelength at your operating frequency and effective Dk (remember that a partially filled print has a lower effective Dk than 2.8):

If the tool returns a wavelength of 6.4 mm at 28 GHz with Dk 2.8, a quarter-wave matching section would be about 1.6 mm thick—easily achievable with current print resolution of ~0.15 mm per layer. At 77 GHz the quarter-wave section is only 0.58 mm, which demands tight layer-height control but is well within the capability of precision dispensing systems.

Dielectric Height and Impedance Considerations

When Radix is printed as a dielectric spacer between a signal trace and a ground plane—essentially forming a microstrip—the height of the printed layer directly sets the characteristic impedance. Thicker layers raise impedance; thinner layers lower it. Because the print process controls height digitally, you can create impedance tapers and transitions that are difficult or impossible with etched laminates.

For a 50 Ω microstrip on solid Radix (Dk 2.8), a trace width of roughly 0.40 mm (16 mil) needs a dielectric height near 0.25 mm (10 mil). Changing the infill to achieve an effective Dk of 2.0 would require a different height to maintain 50 Ω. Use the solver below to explore how dielectric height interacts with impedance for your geometry:

A result showing 0.25 mm for 50 Ω on Dk 2.8 confirms that even a few layers of printed dielectric can establish a controlled transmission line. If your design calls for a thicker spacer—say 0.50 mm for a higher-impedance feed—the tool will show you the corresponding impedance shift so you can adjust trace width or infill accordingly.

Tuning Effective Dk Through Infill Density

One of the most powerful features of Radix printable dielectric is the ability to engineer a custom effective permittivity by controlling infill. A 100 % solid fill gives the full Dk of ~2.8. A 50 % rectilinear infill yields an effective Dk somewhere near 1.9 (a rough volume-average between 2.8 and 1.0 for air). A 25 % infill drops the effective Dk toward 1.4.

This is not a simple linear mixing rule; the field distribution through the lattice matters. Full-wave simulation of the actual infill geometry is recommended for precision designs above 40 GHz. Below that, the effective-medium approximation works well for preliminary sizing.

Practical Infill Guidelines

• Solid fill (100 %): Use for waveguide fills and anywhere you need maximum Dk and mechanical rigidity.
• 70–90 % fill: Good for impedance-matching layers where you want Dk between 2.2 and 2.6.
• 40–60 % fill: Suitable for GRIN lens outer zones and lightweight spacers.
• Below 30 % fill: Structural integrity drops; use only with external support walls.

Integration with Conventional RF Laminates

Radix is not a wholesale replacement for traditional laminates—it is a complement. A typical hybrid build might use a low-loss laminate like Rogers RO3003G2 (Dk 3.00, Df 0.001) for the primary signal layers, with Radix printed on top to form a dielectric lens or a waveguide transition. Bonding between the printed dielectric and the laminate surface requires proper surface preparation—plasma treatment or a thin adhesion-promoting primer—to ensure reliable peel strength.

Thermal management is another integration concern. Radix has a thermal conductivity around 0.25 W/m·K, which is comparable to many PTFE laminates but far below alumina or aluminum-nitride substrates. For high-power applications, consider using CoolSpan TECA film beneath the printed region to conduct heat to a metal core or heat sink.

Design and Fabrication Workflow

1. Define the 3D geometry in your electromagnetic simulator (HFSS, CST, or similar). Export the dielectric volume as an STL or step file.
2. Slice the model using the print system’s slicer, setting infill density per region to achieve the target effective Dk profile.
3. Prepare the substrate: Plasma-clean or prime the laminate surface where dielectric will be deposited.
4. Print and cure: Deposit the Radix material layer by layer, curing each layer (UV or thermal, depending on formulation).
5. Post-process: Inspect dimensions with a profilometer or optical CMM; verify Dk with a split-post dielectric resonator or ring-resonator coupon.
6. Metalize if needed: Sputter or plate conductor patterns onto the printed surface for patch elements or feed lines.

Comparison with Other Approaches to 3D RF Dielectrics

Radix occupies a unique niche: it is the only option specifically formulated for low-loss RF performance and designed to integrate with standard PCB processes. Generic SLA resins may have similar Dk values but typically exhibit higher Df (0.01–0.03 at 10 GHz), making them unsuitable for anything beyond short proof-of-concept runs. LTCC offers excellent high-frequency performance but requires expensive tooling and is limited to high-Dk ceramics, which is the opposite end of the design space from what Radix targets.

Applications and Use Cases

• 5G mmWave base-station antennas: Printed GRIN lenses above patch arrays to improve gain and scan range at 28 GHz and 39 GHz.
• Automotive radar: Compact dielectric waveguide feeds and lens covers at 77 GHz, where traditional radome machining is costly. For the base laminate in these modules, materials like Taconic FastRise 27 pair well with printed dielectric overlays.
• Satellite communications: Lightweight, conformal phased-array lenses for LEO terminal antennas.
• Rapid prototyping: Iterate dielectric geometries in days instead of the weeks needed for custom-machined parts.

Limitations and Trade-Offs

Radix is not a universal solution. Key constraints to keep in mind:

• Print speed: Large-area builds (>100 × 100 mm) can take hours, making volume production challenging without parallel heads.
• Surface roughness: Layer lines introduce surface roughness on the order of 10–30 µm, which can scatter energy above ~100 GHz.
• Dk tolerance: Infill-based Dk tuning depends on mechanical print accuracy; expect ±5 % effective-Dk variation unless you calibrate each build with test coupons.
• Limited vendor ecosystem: As a Rogers-proprietary system, sourcing and support are tied to their additive-manufacturing platform.

For background on how Rogers positions Radix within their broader additive portfolio, see the Rogers additive manufacturing overview.

FAQ

What is the Dk of Radix printable dielectric?

Solid (100 % infill) Radix has a Dk of approximately 2.8 at 10 GHz. By reducing infill density, the effective Dk can be tuned down to roughly 1.4.

Can Radix be used at 77 GHz?

Yes. The material maintains stable Dk and low Df through millimeter-wave frequencies. Surface roughness from the print process should be evaluated above ~60 GHz, as it can introduce scattering loss.

How does Radix attach to a PCB laminate?

The dielectric is printed directly onto a prepared laminate surface. Plasma cleaning or an adhesion-promoting primer ensures reliable bonding. No separate bonding film is needed, though mechanical peel strength should be verified for each substrate combination.

Is Radix suitable for volume production?

Currently it is best suited for prototyping and low-to-medium volume builds. Print speed and per-unit cost are higher than injection-molded or machined dielectrics at scale, but the design freedom and iteration speed often justify the cost in development and specialized applications.

What simulation tools support Radix geometries?

Any 3D full-wave solver—Ansys HFSS, CST Microwave Studio, COMSOL—can import the printed geometry as a CAD solid and assign the appropriate Dk and Df. For infill regions, use the effective-medium Dk value or, for higher accuracy, model the actual lattice structure. Refer to the Ansys HFSS product page for guidance on importing complex dielectric bodies.